We will explore the control of sexual behavior of the fruit fly by the steroid hormone ecdysone. The Drosophila melanogaster model system has produced a quantity of data relevant to higher functions of the human nervous system, including findings in memory processing, sleep, drug abuse and addiction. Exploration of the neurogenetic and hormonal mechanisms controlling sexual behavior in flies will increase our understanding of this important part of human life. Regulation of fruit fly courtship by ecdysone, the fly's only known steroid hormone is previously unknown, despite the wealth of information on courtship behavior. Using a temperature sensitive allele (nonfunctional at 290C) of the ecdysone receptor (EcR) gene we have shown that when EcR activity is impaired in adult males, elevated male-male courtship results (Ganter et al. 2007). We have confirmed the relationship between ecdysone signaling and sexual behavior using the ecd1 temperature-sensitive allele of the ecdysone availability gene ecdysoneless. These results suggest that ecdysone signaling in the adult male is necessary for modulation of sexual motivation, and that sexual behavior is plastic in the adult male fly, neither finding having been shown before. These results establish the fruit fly as a valid model for the study of hormonal control of behavior, with implications extending to higher organisms such as humans. We will now characterize the nature of ecdysone's role in sexual behavior. Specific Aim 1: Characterize the effects of EcR deficiency in brain regions known to be involved in sexual behavior. We will an enhancer trap Gal4 strategy reducing EcR function in courtship initiation regions in the brain, and then assaying for changes in sexual behavior. Specific Aim 2: Characterize the effects of ecdysone signaling hypomorphy on female sexual motivation. Our recent preliminary results suggest that modulation of female sexual motivation may be dependent on ecdysone signaling. We will confirm this result and further test the hypothesis that ecdysone signaling is required for modulation of sexual motivation in adult female flies with a series of experiments focused on female precopulatory behavior. Specific Aim 3: Characterize the developmental profile of ecdysone sensitivity of the adult brain. We will characterize the developmental biology of ecdysone sensitivity by manipulating the ecdysone system at various timepoints and for varying durations. We have implicated this steroid hormone in the modulation of sexual behavior in this tractable model organism, and the results will help us understand how ecdysone carries out this critical reproductive function in the fly, and inform the nature of hormone-behavior connections in higher organisms as well. PUBLIC HEALTH RELEVANCE: The fruit fly is an excellent animal in which to study sexual behavior, and much is known about how flies attract and court their mates. We have shown that sexual behavior in the fly depends on a hormone called ecdysone: when the adult male fly is deprived of the steroid hormone ecdysone, it begins courting other males. Determination of the mechanisms by which ecdysone controls sexual behavior will result in important clues about the normal function of steroid hormones in controlling the sexual behavior of all animals, including humans.